Here is a head scratcher. I heard the "rocks in the transmission" noise while I was on the lake yesterday. Upon investigating my bilge today, I found a piece of a spring that I can only assume (by photos) had to have come from the drive damper. Now the curious question is should I take the boat in to have the damper done, or do I risk further damage continuing to run the boat?

The safest thing is to have it fixed. There are posts and pictures on this forum of damper plates breaking apart and coming through the bell housing. The springs are there to absorb shock and if they are breaking up, it could lead to a complete failure of the plate.

Have a read of this thread, apparently the noise is a common issue but doesn't cause and harm

"Indmar Products
5400 Old Millington Rd. Millington, TN Phone 800-238-7112 Fax 800-622-7278
SERVICE ADVISORY Date: 11/21/01 Advisory #SV2001-2 SUBJECT: Gear Rattle Ė Hurth Reduction Gear Transmissions
We have received a number of complaints regarding rattling or noisy ZF/Hurth reduction gears (V-drive or in-line). The noise is most pronounced at idle RPM and typically goes away when the engine RPM is raised above idle. Although the noise can be irritating, this is a normal condition with these transmissions that in no way affects the durability or reliability of the unit.
In an effort to reduce the gear rattle noise at low RPM; the transmission manufacturer has suggested that we change from the current Dexron 3 transmission fluid that we use in the transmission to 15W40 motor oil. This is the same oil that we recommend for use in the engine and its higher viscosity helps ďdampenĒ the contact of the gears and reduces the noise significantly.
Indmar has started using 15W40 Pennzoil Marine Motor Oil in all reduction gears starting with engine IC985313. Those units will be identified with a Pennzoil 15W40 Marine Oil sticker on the transmission in place of the ATF sticker that was previously attached.
We suggest that if you have a customer complaint of a noisy or rattling reduction gear that you replace the transmission fluid with 15W40 motor oil at the next scheduled service. Our current recommended maintenance schedule calls for changing the transmission oil at the first service (10-20 hours) and then annually or every 300 hours, whichever comes first.
Since the transmission has no drain plug, it is necessary to suck the fluid out of the transmission through the opening in the bottom of the filter cavity. Use a suitable oil removal pump with a pick- up long enough to get to the bottom of the transmission housing. You might also want to remove the coolant lines and let the cooler and hoses drain into a suitable container to make sure as much of the fluid as possible is removed from the transmission. It is not necessary to flush the transmission, just get as much of the old fluid out as possible.
Reconnect the cooling lines and fill the transmission with 15W40 motor oil. The level of the oil should be between the ďmaxĒ and ďminĒ marks on the dipstick. The following chart gives you the approximate capacities of the various reduction gears.
Model Capacity
450A 2.12 qt (2L) 630A 4.2 qt (4L) 630V 4.2 qt (4L)
SV2001-2
11/21/01"

Some are Borg-Warner, some are Hurth. Hurth supposedly will quieten with motor oil but I don't believe Borg-Warner has ever made this recommendation.

The safest thing is to have it fixed. There are posts and pictures on this forum of damper plates breaking apart and coming through the bell housing. The springs are there to absorb shock and if they are breaking up, it could lead to a complete failure of the plate.

Yea, saw some pictures of those drive dampners tearing up bell housings in another thread. Went ahead and took it in yesterday. I just hope what they find confirms my suspicions.

Last Saturday (9/17) I took the boat to try it out but I never got it off the trailer, this was the first time Iíve put it in gear since Iíve owed it and it made a loud clunking while idling in forward and reverse gears. This past Saturday I disconnected the drive couplings so I could dry run it in my driveway and I still had the same noise, it seems to quiet down when I gave it gas. I changed the tranny fluid earlier this year with 15W-40 oil and itís filled up properly. While I had it in the water, a couple of times it stalled just after making a clunk. Iím not sure what to check? When I had the motor out I did not see anything wrong with the pressure plate but then again, I donít really know what I should have been looking for.

click picture to watch video

Some back ground: I bought the boat this spring with spun main bearings so I never heard it run, the boat has 375 hours on it. Any suggestions?

Well Hig, I took my boat into the shop to have the drive dampner replaced. (The drive dampner looks like a clutch pressure plate). I had found pieces of metal and a broken spring that came from the plate in the bilge on top of the strut mount. None of this really affected the transmission performance at all. Figured out the the noise that I was hearing in this instance was those broken pieces funnelling bell housing before they came out. Now, that having been said, the transmission itself is rather noisy especially at low / idle speeds, but sounds smoother when the boat is on plane.

Last Saturday (9/17) I took the boat to try it out but I never got it off the trailer, this was the first time Iíve put it in gear since Iíve owed it and it made a loud clunking while idling in forward and reverse gears. This past Saturday I disconnected the drive couplings so I could dry run it in my driveway and I still had the same noise, it seems to quiet down when I gave it gas. I changed the tranny fluid earlier this year with 15W-40 oil and itís filled up properly. While I had it in the water, a couple of times it stalled just after making a clunk. Iím not sure what to check? When I had the motor out I did not see anything wrong with the pressure plate but then again, I donít really know what I should have been looking for.

Some back ground: I bought the boat this spring with spun main bearings so I never heard it run, the boat has 375 hours on it. Any suggestions?

Thanks, Steve

That doesn't sound good to me at all, Steve. These transmissions are noisy, but definitely not like that. Something has to be out of kilter. I know the history on you boat is a bit unknown, except for the main bearing on the engine, but the drive train had to have taken a hit as well judging by bent strut in you restoration thread. Granted I've only had my MC for 3 years now, and I am still learning things about it. I am not an expert by any means, so I have no idea how much shock it would take to bend a strut. When the engine spun that bearing, did it cease? Could the shock from that affect the transmission? Maybe I'm getting a bit off topic here; just brainstorming. In any case, I'd consider taking the transmission back out and take it in for service.

That doesn't sound good to me at all, Steve. These transmissions are noisy, but definitely not like that. Something has to be out of kilter. I know the history on you boat is a bit unknown, except for the main bearing on the engine, but the drive train had to have taken a hit as well judging by bent strut in you restoration thread. Granted I've only had my MC for 3 years now, and I am still learning things about it. I am not an expert by any means, so I have no idea how much shock it would take to bend a strut. When the engine spun that bearing, did it cease? Could the shock from that affect the transmission? Maybe I'm getting a bit off topic here; just brainstorming. In any case, I'd consider taking the transmission back out and take it in for service.

Joe

Thanks for the information that mine is a lot louder than yours, last think I want to do is send something thru the case and end up having to replace the trans not just fix it.

I have no idea about the past history except it had to of had a hard 375 hours!!! I don't think the bent strut is related because the boat was driven for a while after it was bent to wear thru the shaft log like it did. The main bearing must have heated up quite a bit, the crank was warped and a couple of main caps were spread out from the heat so I'm assuming it seized up.

I figured with a bad motor the trans MUST be good otherwise they would not have been using but who know.

If anything I would pull the trans and split the case (after doing some research) to see if I can see any damage inside.

Does everyone agree that's what I should do? Or do I have any other options?